Gravity flow systems, such as sewer systems, regularly require maintenance or repair and it is well known to block, or isolate, a sewer pipe from fluid flowing therethrough, to allow the necessary work to be carried out downstream from the blockage. The plugs in common usage for creating the necessary blockage are expandable or inflatable plugs, an example of which is the Muni Ball® manufactured by Cherne Industries, Inc. of Minnesota U.S.A. This inflatable plug includes an inflatable central portion capped at each end by steel plates. The central portion is inflated using pneumatic pressure to grip the interior surface of the pipe, thereby preventing fluid flow therethrough.
There are considerable problems associated with such inflatable plugs. Firstly, there are problems associated with the under-pressure of the plug i.e. when insufficient pneumatic pressure is supplied, for example in the event of failure of the pneumatic pump. In this case, the sealing grip of the inflatable portion against the interior surface of the pipe will be lost leading initially to undesirable leaks and then ultimately to the potentially high speed projection of the plug within the pipe as a result of water pressure which may have built up behind the plug. The projectile plug can then travel, with considerable force and energy, towards the workers in the downstream section of the pipe, which is obviously highly undesirable. To avoid such problems, it is intended that an inflatable plug is used in conjunction with a restraint but such restraints may be readily omitted by a user. Secondly, there are problems associated with over-pressurisation of the plug. If too much pressure is applied by the pneumatic pump, the inflatable portion may over-inflate to such an extent that it can burst, or otherwise fail. This will lead to a flood of water towards any workers present down-stream of the plug, together with high-speed projection of the remains of the plug, as a result of both the build-up of water pressure and the bursting action of the plug. Several workers have lost their lives as a result of an inflatable plug bursting or failing in such a manner.
In attempt to protect workers in such conditions, it is recommended that an exclusion area is created around the plug. It is also recommended that the pressure supplied to the plug be continuously monitored to ensure that under- or over-pressure does not occur. Adhering to both of these recommendations can be inconvenient for workers, particularly when space requirements are at a premium to make exclusion areas difficult to maintain and when personnel is limited to allow for constant monitoring of pressure supply levels.
Finally, the requirement for the provision of a compressor to provide compressed air to inflate the plug can be inconvenient as it is necessary to transport the compressor to the location of an access shaft of the gravity flow system and access shafts may be located in rough or steep terrain.
The present invention is directed towards providing a device for isolating a pipe, or sections of a pipe, which substantially ameliorates the problems associated with the known inflatable plugs.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.